In nuclear facilities such as nuclear fuel processing plants, constant vigil is required to prevent the inadvertent discharge of radioactive wastes into the surrounding environment. The possible presence of radioisotopic particles in liquid waste streams is of particular concern. The release of even very low level radioactive liquid waste constitutes an environmental hazard. Thus, the liquid waste stream must be assayed to detect the presence of extremely low concentrations of radionuclides. Radioactivity monitoring has been accomplished by taking random samples of the liquid waste stream and testing for the presence of radionuclids in a laboratory. If the flow of liquid waste is continuous, significant quantities of potentially radioactive liquid waste can be discharged into the environment during the intervals between random tests. This approach is therefore unacceptable.
Thus to satisfy regulatory standards, the liquid waste stream must be monitored for radioactivity on a 100% basis. If the volumetric flow of the liquid waste stream is large, reliable 100% testing can pose a significant bottleneck to efficient plant operation. Continuous radioactivity monitoring of the liquid waste as it is being discharge into the surrounding environment may require that the flow rate be throttled down to ensure requisite accuracy. Alternatively, the liquid waste may be accumulated in holding tanks, and samples are taken from the tanks for laboratory testing. The tanks are then discharged if the concentrations of radionuclides are found to be acceptably low. This approach certainly satisfies the 100% testing criteria and is reliable if the tested samples accurately represent the compositions of liquid waste in the holding tanks. However, it is not particularly expeditious. Thus, so as not to curtail plant operations, numerous large holding tanks are required to keep up with a waste stream of significant volumetric flow rate.